The present invention relates generally to air bag systems for use as safety devices in automotive vehicles and, more particularly, to a backup power supply system for a restraint control module.
Over the past several years, there has been a trend in the automotive industry to install air bag systems in vehicles to enhance protection traditionally afforded vehicle occupants through the use of seat belts. In some automotive vehicles, the inflatable restraint system may be an air bag system disposed within an occupant compartment in the automotive vehicle in close proximity to either a driver occupant or one or more passenger occupants. Usually, the air bag system includes a restraint control module that is connected to the vehicle structure and an air bag for deployment through an opening in a cover to extend and inflate in an occupant compartment of the automotive vehicle. The deployed air bag restrains movement of the occupant to protect the occupant from forcefully hitting parts of the automotive vehicle as a result of an automobile accident.
Air bag systems typically include a restraint control module, a reaction canister and an air bag and inflator that are stored inside the reaction canister. Generally speaking, the inflator is actuated by a signal received from a vehicle deceleration sensor or accelerometer that is connected to the restraint control module, which, in turn, causes a discharge of inflator gas into the interior of the air bag. The restraint control module controls the overall operation of the air bag system and essentially could be viewed as the main control unit for the air bag system.
As with any system based on electronic components and sensors, air bag systems and their associated electronic components, require power from a power supply in order to function properly. During normal operation, the power used to drive an air bag system and its related components originates from a battery that is located in the automotive vehicle. During some automotive accidents, the electrical conductors that connect the battery to the air bag system and its related electronic components may become severed or damages so that power is cut off to these systems. As a result of the conductor being severed or damaged, the electronic components of the air bag system lose power and will not function properly due to the loss of power. As such, a need exists in the automotive industry for methods and systems of providing backup power to the air bag system.
The present invention discloses a backup power supply system for a restraint control module. The preferred backup power supply system includes a main power source that is connected to a backup power source charging circuit as well as the restraint control module. During normal operation, the main power source provides power to the restraint control module. A backup power source is connected to the backup power source charging circuit and the restraint control module. A boost converter control and driver circuit is connected to a boost converter switching device, which is, in turn, connected to the backup power source charging circuit. During normal operation, the boost converter control and driver circuit switches the boost converter switching device to charge the backup power source with the main power source using the backup power source charging circuit.
A backup power supply control and driver circuit is connected to a backup power supply switching device as well as the boost converter control and driver circuit. The backup power supply control and driver circuit uses the backup power supply switching device to switch the source of power to the restraint control module from the main power source to the backup power source if a loss of power is sensed from the main power source. The backup power supply control and driver circuit is connected to the boost converter control and driver circuit to ensure that the booster converter control and driver circuit does not attempt to charge the backup power source while it is providing power to the restraint control module in the event of a power loss.
In the preferred embodiment, the backup power supply charging circuit comprises an inductor that is electrically connected to the main power source and the backup power source. During normal operation, the inductor is pulse width modulated using the boost converter switching device to charge the backup power source. The backup power source comprises a capacitor that is preferentially sized to charge to a predetermined voltage within six seconds of startup of the vehicle.
The preferred backup power supply system may also include a voltage regulator that is connected to the output of the backup power source and the boost converter control and driver circuit. The voltage regulator is used to regulate the output voltage generated by the backup power source while the backup power source charging circuit is charging the backup power source. The preferred voltage regulator comprises an error amplifier connected to a pulse width modulator comparator.
The backup power supply system may also include a charge pump circuit that is connected to the output of the backup power source. The charge pump circuit includes a charge pump that is used in the preferred embodiment to generate a plurality of gate drive voltages that are higher than the voltage present on the backup power source. The gate drive voltages may then be used to drive internal and external high side switches effectively.
An over-current protection circuit is also included in the preferred backup power supply system and is connected to the boost converter switching device and the boost converter control and driver circuit. The over-current protection circuit causes the boost converter control and driver circuit to stop switching the boost converter switching device to charge the backup power source if a predetermined current threshold is exceeded.